The proof of a link suggests that at least some of the 961,000 deaths from heart disease in the United States every year could be prevented by treatment with antibiotics or, even better, by immunization against the responsible organisms.
It might also lead to new ways to identify people at the highest risk of death, experts said.
In the new study, to be reported today in the journal Science, researchers from the Ontario Cancer Institute in Toronto found that injecting mice with proteins from chlamydia bacteria can produce heart disease. As many as 95 percent of people are exposed to chlamydia during their lives.
The chlaniydia protein, which sits on the bacteriium's surface, is virtually identical to one found in healthy heart tissue. When the mouse's immune system[ gears up to attack the protein, it also damages the heart and coronary arteries.
"Ours is the first experimental proof to show how bacterial infection can lead to heart disease," said Dr. Josef M. Penninger of the Ontario Cancer Institute. "The results nearly knocked me off my chair."
The results do not mean that high cholesterol, smoking, obesity and hypertension are not important factors in heart disease, said Dr. Paul Ridker of the Harvard Medical School. Rather, the findings add one more risk factor to the constellation of health problems that lead to heart attacks.
Though Ridker and some others do not believe that the case against chiamydia has been conclusively proved, they are supporting human trials to see if antibiotics can prevent some heart attacks. "The public health importance is large enough that well- designed clinical trials (of antibiotic therapy) are worth the effort," he said.
Already, three large trials enrolling more than 8,000 heart disease patients are under way to determine if antibiotics effective against chlamydia reduce the risk of heart attacks.
One of those trials is directed by Dr. P.K. Shah of the Cedars-Sinai Medical Center in Los Angeles. He thinks the new results "may be enough to tip the balance" of evidence toward the idea that bacteria cause heart disease.
But, he added, "The proof is still going to be in the pudding. We won't be sure until we see the results of the clinical trials."
The idea that infection can cause heart disease is not new. The streptococci bacteria that cause rheumatic fever also attack the heart, causing lingering damage. Several viruses attack the heart directly, producing myocarditis, which is often fatal.
Staphylococcal and streptococchal bacteria also have been shown to cause Kawasaki syndrome, a disorder of children that is marked by severe heart disease.
But those conditions are rare. Now some scientists are beginning to believe that infections may play a role in the vast majority of heart disease patients, perhaps as many as 80 percent of all cases. But pinning down those links has proved elusive.
There have been many findings hinting at such a link. As many as 20 percent of heart attack victims, for example, do not have any of' the known risk factors for heart disease, according to Dr. Marvin 1. Dunn of' the University of' Kansas School of' Medicine in Kansas City.
. Moreover, blocked coronary arteries show strong evidence of inflammation - an accumulation of white blood cells resulting from an immune attack on an infectious agent.
Ridker has shown that the risk of' heart attack can be predicted by measuring the levels of so-called Creactive protein, which is also produced in the inflammatory process caused by infections.
Many infectious agents have been tentatively linked to heart disease. Among them are: bacteria from the mouth, which can cause blood to clot; cytomegalovirus, a herpes virus that causes blindness; and "Helicobacter pylori," which causes ulcers.
But much of the focus has recently shifted to "Chlamydia pneumoniae" and its close relatives, "C. psittaci" and "C. trachomatis."
Friday, Feb. 26, 1999 Houston Chronicle 19A